GEOGRAPHICAL DISTRIBUTION 185 



swallow seeds of moderate size, as of the yellow water- 

 lily and Potatnogeton. Herons and other birds, century 

 after century, have gone on daily devouring fish; they 

 then take flight and go to other waters, or are blown 

 across the sea; and we have seen that seeds retain their 

 power of germination, when rejected maay hours after- 

 ward in pellets or in the excrement. When I saw the 

 great size of the seeds of that fine water-lily, the JNelum- 

 bium, and remembered Alph. de Candolle's remarks on 

 the distribution of this plant, I thought that the means 

 of its dispersal must remain inexplicable; but Audubon 

 states that he found the seeds of the great south- 

 ern water-lily (probably, according to Dr. Hooker, the 

 Nelumbium luteum) in a heron's stomach. Now this 

 bird must often have flown with its stomach tlius well 

 stocked to distant ponds, and then getting a hearty meal 

 of fish, analogy makes me believe that it would have re- 

 jected the seeds in a pellet in a fit state for germination. 

 In considering these several means of distribution, it 

 should be remembered that when a pond or stream 

 is first formed, for instance, on a rising islet, it will be 

 unoccupied; and a single seed or egg will have a good 

 chance of succeeding. Although there will always be a 

 struggle for life between the inhabitants of the same 

 pond, however few in kind, yet as the number even in 

 a well-stocked pond is small in comparison with the num- 

 ber of species inhabiting an equal area of land, tlie com- 

 petition between them will probably be less severe than 

 between terrestrial species; consequently an intruder from 

 the waters of a foreign country would have a better 

 chance of seizing on a new place than in the case of 

 terrestrial colonists. We should also remember that many 



